1. Field of the Present Invention
The present invention relates to a laminated electronic component and a method for manufacturing the laminated electronic component, and more particularly, to a structure of an external terminal electrode and a method for forming the external terminal electrode.
2. Description of the Related Art
As shown in FIG. 3, a laminated electronic component 101 typified by a laminated ceramic capacitor generally includes a component main body 105 having a laminated structure, which includes a plurality of laminated insulator layers 102 composed of, for example, a dielectric ceramic, and a plurality of layered internal electrodes 103 and 104 formed along interfaces between the adjacent insulator layers 102. Respective ends of the plurality of internal electrodes 103 and respective ends of the plurality of internal electrodes 104 are exposed at one end surface and the other end surface 106 and 107 of the component main body 105, and external terminal electrodes 108 and 109 are respectively arranged so as to electrically connect the respective ends of the internal electrodes 103 to each other and the respective ends of the internal electrodes 104 to each other.
For the formation of the internal terminal electrodes 108 and 109, in general, a metal paste including a metal component and a glass component is applied onto the end surfaces 106 and 107 of the component main body 105, and then baked, thereby first forming baked metal layers 110. Next, first plating layers 111 primarily including, for example, nickel, are formed on the baked metal layers 110, and second plating layers 112 primarily including, for example, tin or gold are further formed thereon. Thus, each of the external terminal electrodes 108 and 109 is formed in a three-layer structure including the baked metal layers 110, the first plating layer 111, and the second plating layer 112.
The external terminal electrodes 108 and 109 are required to have excellent solderability when the laminated electronic component 101 is mounted on a substrate using solder. At the same time, the external terminal electrode 108 is required to have a function of electrically connecting each of the plurality of internal electrodes 103 which are electrically insulated from each other, and the external terminal electrode 109 is required to have a function of electrically connecting each of the plurality of internal electrodes 104 which are electrically insulated from each other. The second plating layers 112 described above ensure the solderability, whereas the baked metal layers 110 electrically connect the internal electrodes 103 to each other and the internal electrodes 104 to each other. The first plating layers 111 prevent solder erosion in solder joint.
However, the baked metal layer 110 has a relatively large thickness from several tens of μm to several hundreds of μm. Therefore, in order to limit the dimensions of the laminated electronic component 101 within certain specifications, there is undesirably a need to reduce the effective volume for ensuring a capacitance because there is a need to ensure the volumes of the baked metal layers 110. On the other hand, the plating layers 111 and 112 have a thickness on the order of several μm. Thus, if the external terminal electrodes 108 and 109 can be composed only of the first plating layers 111 and the second plating layers 112, the effective volume for ensuring the capacitance can be increased.
For example, Japanese Unexamined Patent Publication No. 2004-146401 discloses a method in which a conductive paste is applied to at least ridge sections of end surfaces of a component main body along the direction of laminating internal electrodes so as to come into contact with leading sections of the internal electrodes, the conductive paste is baked or thermally cured to form a conductive film, and further, the end surfaces of the component main body are subjected to electroplating, thereby forming an electroplating film so as to be connected to the conductive film on the ridge sections. According to this method, the thickness of external terminal electrodes at the end surfaces can be reduced.
Furthermore, Japanese Unexamined Patent Publication No. 63-169014 discloses a method in which a conductive metal film is deposited by electroless plating on the entire sidewall surface of a component main body, at which internal electrodes are exposed, so as to short circuit the internal electrodes exposed at the sidewall surface.
However, in the methods for forming external terminal electrodes as described in Japanese Unexamined Patent Publication No. 2004-146401 and Japanese Unexamined Patent Publication No. 63-169014, plating is performed directly onto the ends at which the internal electrodes are exposed. Thus, a plating solution entering the component main body along the interfaces between the internal electrodes and the insulator layers may erode the ceramic defining the insulator layers and the internal electrodes, thereby causing structural defects. Furthermore, this results in defects in terms of reliability, such as degraded load characteristics against humidity for the laminated electronic component.
In particular, when tin or gold plating is to be applied, the problems described above are more likely to occur because a tin or gold plating solution generally contains a highly corrosive complexing agent.
In order to solve the problems described above, for example, the International Publication No. WO2007/119281 discloses applying a water repellent to end surfaces of a component main body at which respective ends of internal electrodes are exposed, to fill gaps at interfaces between insulator layers and the internal electrodes with this water repellent, and then, directly forming metal layers defining bases of external terminal electrodes by plating on the end surfaces. The application of such a water repellent can improve the lifetime characteristics in the load test against humidity.
However, the technique described in International Publication No. WO2007/119281 has the following problems.
The water repellent is likely to adhere to the ceramic sections provided by the insulator layers rather than the metal sections provided by the internal electrodes. If the distance between the internal electrodes is relatively large (that is, when the insulator layers are thick and the number of laminated internal electrodes is small), most portions of the end surfaces at which the respective ends of the internal electrodes are exposed will be covered with the water repellent, thereby decreasing the depositions plated to the end surfaces at which the internal electrodes are exposed.
Furthermore, for the purpose of improving the fixing strength of the external terminal electrodes to the component main body, a heat treatment may be performed at a temperature of 800° C. or more after the formation of the metal layers. However, such a heat treatment will cause the water repellent to disappear.
Moreover, for example, International Publication No. WO2008/023496 suggests forming metal layers defining bases of external terminal electrodes by plating on end surfaces of a component main body at which respective ends of internal electrodes are exposed, and then forming layers composed of a conductive resin on the metal layers. International Publication No. WO2008/023496 also discloses that metal layers composed of nickel or copper are formed on the conductive resin layers by plating in order to prevent solder erosion upon solder joint, and that metal layers composed of tin or gold are further formed thereon by plating in order to improve solderability.
According to the technique described in International Publication No. WO2008/023496, with the metal layers formed by plating as bases, the conductive resin layers are formed thereon. Thus, stress caused by deflection of a substrate mounted with the laminated electronic component is reduced, thereby reducing crack defects.
However, the technique described in International Publication No. WO2008/023496 has the following problem.
As described above, a tin or gold plating solution generally contains a highly corrosive complexing agent. Thus, for example, if the treatment for providing water repellency is to be performed as described in International Publication No. WO2007/119281, it is necessary to perform the treatment for providing water repellency before the plating step of forming the metal layers composed of tin or gold. However, for example, when a treatment for providing strong water repellency is performed after the formation of the conductive resin layers, plating adhesion onto the conductive resin layers will be deteriorated, and problems such as no plating adhesion will be likely to occur. Particularly when the metal layers defining bases of the external terminal electrodes are formed directly by plating as in the technique described in International Publication No. WO2008/023496, rather than by baking, this problem will become more serious because the use of a water repellent with strong water repellency is desired.
It is to be noted that it is not a known technique but just a hypothetical technique suggested by the inventor(s) of the present application to further perform the treatment for providing water repellency to the external terminal electrodes with the conductive resin layers having been formed.